Optical and Electrical Properties of CuO-MnO2-B2O3 Glasses

International Research Journal of Advanced Engineering and Science ISSN (Online): 2455-9024

Optical and Electrical Properties of CuO-MnO2-B2O3 Glasses W. J. Gawande1, S. S. Yawale2, S. P. Yawale3 1, 3 2

Government Vidarbha Institute of Science and Humanities, Amravati, Maharashtra, India-444604 Director, Govt. Vidarbha Institute of Science and Humanities, Amravati, Maharashtra, India-444604

Abstract— The optical absorption and transmission spectra in (UV-

absorption, Infrared, differential thermal analysis and density studies were conducted on the glass system (80-X) TeO2XNiO2-20B2O3 by Khaled et al. [8]. The divalent state of Ni has been confirmed by IR spectra. The optical properties of the CaO-Al2O3-B2O3 glasses are reported by Kudesia et al. [9].

Linear and non-linear optical properties of chalcogenide glass were investigated by Hajita et al. [10]. Very little work appears to have been done on the optical properties of oxide glasses. Therefore it has been decided to study the optical parameters of CuO-MnO2-B2O3 glasses. The intention to study the optical properties of these glasses by UV-VIS spectra is to investigate the existence of localized states near band edge.

Ghosh et al. [13] discussed the results of dc-conductivity of semiconducting vanadium bismuth oxide, containing 80-95 mol% vanadium pentaoxide in the 300-500 K temperature range on the basis of polaronic hopping model similarly they observed adiabatic hopping conduction. The electrical properties of V2O5-B2O3 glasses are discussed on the basis of small polaron hopping model by Culea et al. [14]. The charge transfer mechanism plays a dominant role in semiconducting glasses. Dc-conducting and hopping mechanism in Bi2O3B2O3 glasses has been studied by Yawale et al. [15]

VIS) have been recorded in the wavelength range 350-800 nm for different compositions of CuO-MnO2-B2O3 glasses. The various optical properties such as absorption coefficient (’), optical energy gap (Eopt), refractive index (no), optical dielectric constant (’), measure of extent of band tailing (E), constant () and ratio of carrier concentration to the effective mass (N/m*) for different glasses have been reported. The effects of composition of glasses on these parameters have been discussed. It has been indicated that a small modification of the glasses can lead to an important change in all the optical properties. These results are interesting showing non linear behaviour for all these parameters investigated. The optical parameters are found to be almost the same for different glasses in the same family. Due to the technological importance of CuO-MnO2B2O3 glasses, dc-conductivity measurement with increasing concentration of MnO2 (in the range of 5-30 mol%) have been reported in the temperature range of 313-573 K in the present study.

A plot of –log  versus 1/T shows two different regions of conduction suggesting two types of conduction mechanisms switching from one type to another occurring at knee temperature. The DC conductivity increases with increase in temperature of the sample and also with increase of mol% of MnO2. Activation energy calculated from both regions (LTR and HTR) is below 1 eV. Thus electrical conduction is electronic. Activation energy in LTR and HTR are temperature independent but composition dependent.

II. Keywords— CuO-MnO2-B2O3 glasses, Optical properties, nonlinear behavior, DC-conductivity.

I.

EXPERIMENTAL DETAILS

A. Preparation of Glass Samples The glass samples under investigation were prepared in a fireclay crucible. The muffle furnace used was of Heatreat co.

Ltd. (India) operating on 230 volts AC reaching upto a maximum temperature of 1500 + 10°C. Glasses were prepared from AR grade chemicals. Homogeneous mixture of an appropriate amounts of CuO, MnO2 & B2O3 (mol%) in powder form was prepared. Then, it was transferred to fireclay crucible, which was subjected to melting temperature (1300°C). The duration of melting was generally two hours.

The homogenized molten glass was cast in steel disc of diameter 2 cm and thickness 0.7 cm. Samples were quenched at 200°C and obtained in glass state by sudden quenching method. All the samples were annealed at 350°C for two hours. The X-ray diffractograms of all the glass samples are determined at regional sophisticated instrumentation center, Nagpur. The absence of peak in the X-ray spectra confirmed the amorphous nature of the glass samples.

INTRODUCTION

In the recent years, the interest in the study of electrical, optical and structural properties of glassy semiconductors has increased [1] considerably. The variation of optical density of a few induced absorption bands in some sodium aluminium borate glasses has been studied by varying the radiation doses of gamma rays and cerium content by Hussein et al. [2]. On the basis of the optical absorbance and transmittance measured at normal incidence of light in wavelength range 380-780 nm. some optical parameters of glassy Ge20 Te80-x Sex thin films were determined by Shokr et al. [3]. Optical and electrooptical properties of Ga2O3-PbO-Bi2O3 glasses were studied

by Janewioz et al. [4]. Anomalous behaviour in the composition dependence of the photoacoustic properties of SiAs-Te glasses has been studied by Srinivasan et al. [5]. The frequency dependent optical and dielectric properties of binary semiconducting glasses in the system 60V2O5-(40-X)TeO2XPbO were measured as a function of lead content by Memon et al. [6]. Studies on the optical properties and structure for SiO2-TiO2-PbO2 system glass were reported by Zhu et al. [7].

A structural model of the glass network was proposed. Optical

B. Electrical Measurement The dc resistance of the glass samples was measured by using D.C. microvoltmeter, Systronics 412 India; having an accuracy of ±1 V and input impedence 10 M, by voltage 85

W. J. Gawande, S. S. Yawale, and S. P. Yawale, ―Optical and electrical properties of CuO-MnO2-B2O3 glasses,‖ International Research Journal of Advanced Engineering and Science, Volume 2, Issue 3, pp. 85-88, 2017.

International Research Journal of Advanced Engineering and Science ISSN (Online): 2455-9024

drop method given by Kher et al. [16]. Before electrical measurements all the samples were polished to smooth surfaces using fine quality emery paper. After application of conducting silver paint at either sides, the samples were used for electrical measurements. The silver paint acts like electrodes for all the samples.

III.

The reflectance R was calculated using the equation t = (1 - R)2 exp (-A)

(2) where R is the reflectance, ‗t‘ is the transmittance and ‗A‘ is the absorbance.

The relation between optical dielectric constant, ‘ and the square of the wavelength ‘2, is given by 1  R  e2 N ' 2 (3)  ‘  n2   . .    ‘   C 2 m* 1  R  where ‘ is the dielectric constant, e is the electronic charge and N/m* is the ratio of carrier concentration to the effective mass. By knowing the values of absorbance A reflectance and transmittance and various optical properties were calculated.

THEORY

The absorption ‗A‘ and transmittance ‗t‘ of the glass samples were measured by means of CARY –2390 varaian make double beam automatic scanning spectrophotometer (at Regional sophisticated Instrumentation Centre, Madras) in the spectral range 350-800 nm at normal incidence. The glass powder pellet thickness used was approximately 0.05 mm at room temperature. The resolution of the instrument used was 0.1 nm. The optical absorption coefficient ‘ of the glass samples was calculated from the relation A = ‘ x d‘ where d‘ is the thickness of pellet. The spectral dependence of both A and t on composition of the glasses is shown in figure (1)

Fig. 2 . Plot of ‘h verses h for samples GB1, GB2, GB3, GB4, GB5, GB6.

IV.

RESULTS AND DISCUSSION

A. Optical Properties The results regarding the various optical properties such as optical energy gap (Eopt), constant , measure of extent of band tailing (E), mean refractive index n0, infinitely high frequency dielectric constant ‘ and ratio N/m* for different glasses are listed in table (I). Figure (2) Shows the plots (h)1/2 versus h for different compositions of glass samples.

The most satisfactory representation is obtained by plotting the quantity (h)1/2as a function of h. Similar behaviour was also observed by other workers [11]. The observed behaviour suggests forbidden indirect transition for some glassy and amorphous material. The values of optical energy gap E opt obtained from the extrapolation of the linear region and constant  from the slopes of the derived curves.

Fig. 1. Spectral dependence of both absorbance and transmittance for six different samples GB1, GB2, GB3, GB4, GB5, GB6.

The optical absorption coefficient ‘() at the given frequency () is given by  4 min (hv  Eopt )  ‘(v)  .

(1) Cn0 E hv Where min is the extrapolated dc-conductivity at T = , n0 is the refractive index, C is the velocity of light, E is the measure of the extent of band tailing, h is the photon energy, Eopt is the optical gap,  = 2 is a number which characterises the transition process, and 4 min  Is constant C.no E

TABLE I. The values of optical energy gap (Eopt) dielectric constant at infinite frequency (‘), refractive index (no), constant (), measure of the extent of band tailing (E) and the ratio of carrier concentration to the effective mass (N/m*) for different glass compositions.

Constant Measure of Infinitely high Ratio of carrier Mean Optical energy extent of band frequency concentration to Glass composition refractive  gap Glass tailing dielectric effective (mol%) index (cm-1eVEopt(eV) No. 1/2 mass N/m* (cm-3) x 1021 no ) E(eV) constant ‘ CuO MnO B2O3 GB1 20 5 75 2.24 282.24 0.088 1.66 9.6 3.80 GB2 20 10 70 0.56 36.00 0.185 2.58 10.2 1.84 GB3 20 15 65 0.32 36.00 0.150 2.72 10.8 1.72 GB4 20 20 60 0.87 36.00 0.070 3.25 20.0 4.91 GB5 20 25 55 0.12 31.36 0.344 3.56 22.4 5.40 GB6 20 30 50 0.10 36.00 33.21 3.72 22.8 4.66

86 W. J. Gawande, S. S. Yawale, and S. P. Yawale, ―Optical and electrical properties of CuO-MnO2-B2O3 glasses,‖ International Research Journal of Advanced Engineering and Science, Volume 2, Issue 3, pp. 85-88, 2017.

International Research Journal of Advanced Engineering and Science ISSN (Online): 2455-9024

The extrapolated dc electrical conductivity, min at t =  is obtained from the plot of logversus 1/T (plot not shown).

The values obtained for Eopt for the six different compositions of glass samples are found to be non-linear. Similar observation are reported in case of As-S, Ge-Se, As-Se and Ag-As systems investigated by Hajto et al. [10].

The dielectric constant ‘ versus ‘2 plots shown in Figure (3) are linear, verifying equation (3), Values of ‘ and N/m* determined from the extrapolation of these plots at ‘ = 0 and the values of the ratio of carrier concentration to effective mass are listed in table I as a function of glass composition.

The dependence of refractive index and dielectric constant on composition of glasses is rather non-linear and is observed to be similar to other amorphous materials [10]. The values of refractive index no are calculated from optical dielectric constant ‘ for all the wavelengths of ‘.

The average value of refractive index no shows dependence on MnO2 composition.

The variation of E, the width of the tail of localised states in the normally forbiden gap against MnO2 (mol %) is shown in Figure (4). The optical energy gap Eopt is found to be minimum for the glass sample having 30 (mol %) of MnO2 and E for 20 (mol %) of MnO2. The decreasing trend of the band tailing energy suggests the presence of sharp localised states in the ratio of carrier concentration to the effective mass. N/m* has been calculated from the slope of the plot ‘ versus ‘2 (Fig. 3). The values of N/m* for different glass samples are tabulated in Table I. It has been observed that the values are found to be of the order of 1021 which are in agreement with the values reported by other workers for oxide glasses [12] and calculated by other methods. The value of E shows dip at 20 mol% and peak at 10 mol% of MnO2. It is observed that the nature of plot of Eopt and E verses composition is opposite to each other. The decreasing trend of the band tailing energy suggests the presence of sharp localized states in the band gap.

The ratio of carrier concentration to the effective mass, N/m* has been calculated from the slope of the plot ‘ verses ‘2 B. Dc-electrical Conductivity D.C. electrical conductivity of the glass samples is measured in the temperature range 313 to 573 K. The value of d.c. conductivity is found to be of the order of 10 -10 to 10-11 ohm-1 cm-1 at 313 K. Fig 5 shows the plot of -log  versus 1/T. It is observed that, the conductivity of all the glass samples studied increases with increasing temperature.

This plot is found to consists of two distinct straight linear regions called as low temperature regions (LTR) (313 to 413 K) and high temperature region (HTR) (523 to 573 K). In LTR conductivity increases linearly with increasing temperature at very slow rate where as in HTR conductivity increases linearly with increasing temperature at a faster rate. Obviously two activation energies and two conduction mechanisms are associated with electronic conduction in all the glasses studied. The same type of dc conductivity behaviour is reported in literature [15, 17, 18]. The activation energies are obtained from slope of the plot of log  versus 1/T in both the regions and reported in table II. It is observed that the activation energy is temperature independent but depends on composition.

Fig. 3. Plot of optical dielectric constant ‘ verses ‘2 for six samples GB1, GB2, GB3, GB4, GB5, GB6.

Fig. 4. Plot of optical energy gap Eopt and band tailing energy E verses mol% of MnO2 composition of six samples.

These values are found to be more or less same throughout the wavelength range (350-800 nm).

Therefore average values of no are reported in this wavelength region.

Glass No. G B1 G B2 G B3 G B4 G B5 G B6

TABLE II. Activation energies, Kink Temperature and Pre- exponential factor o of CuO-MnO2-B2O3 glasses.

Activation energy W (eV) Kink Tempera-ture Activation energy at c Pre-exponential factor o Composition (mol%) LTR HTR CuO-MnO2-B2O3 c (K) W (eV) (ohm x cm) -1 10-9 (WL) (Wh) 20-5-75 0.0035 0.250 476 0.0754 15.8 20-10-70 0.0052 0.181 471 0.0603 6.60 20-15-65 0.0060 0.258 456 0.0517 5.62 20-20-60 0.0069 0.310 450 0.0431 3.16 20-25-55 0.0086 0.422 440 0.0388 14.7 20-30-50 0.0090 0.474 378 0.0345 1700

87 W. J. Gawande, S. S. Yawale, and S. P. Yawale, ―Optical and electrical properties of CuO-MnO2-B2O3 glasses,‖ International Research Journal of Advanced Engineering and Science, Volume 2, Issue 3, pp. 85-88, 2017.

International Research Journal of Advanced Engineering and Science ISSN (Online): 2455-9024

The activation energies obtained are found to be of order of borate vanadate and other semiconducting glasses reported in literature [12], [19-22]. Activation energy calculated for both regions (LTR and HTR) is found to be less than 1 eV, thus the electrical conduction is electronic.[23] The kink temperature c is the temperature at which the Arrhenius plot is divided in to two linear regions of different slopes. The kink temperature (c) is determined from the plot of –Log  versus 1/T and is reported in table II. The kink temperature c for the series of glasses studied decreases with increasing mol% of MnO2. The activation energy is also calculated at kink temperature and the values are reported in table II. The inetecept on –log  axis of - log  versus 1/T plot gives the values of pre-exponential factor (–log 0) Table II reports the values of activation energy, kink temperature, pre-exponential factor of CuO-MnO2-B2O3 glasses. The values of different parameters reported in the table agreed with the values reported for semiconducting glasses in the literature [12, 15, 19-22]. Fig. 6 shows the variation of activation energy (w) with MnO2 mol% in LTR and HTR for the glass samples. Fig. 7 shows variation of preexponential factor (-logσ0) versus Composition for the glasses studied.

high frequency dielectric constant and ratio of carrier concentration to the effective mass are found to be composition dependent. The linear behaviour is observed in (‘h)1/2 with h suggesting forbidden indirect transition. The value of optical energy gap (Eopt)are found to be non-linear with composition. Non-linear behaviour is observed in measures of the extent of band tailing (E) with composition (mol%). The ratio of carrier concentration to the effective mass (N/m*) is found to be to the order of 10 21 cm-3. D.C. conductivity of CuO-MnO2-B2O3 glass system is studied in the temperature range 313-573K. The activation energy are found to be in the range of semiconducting glasses. The electrical conduction is electronic.

ACKNOWLEDGEMENT Authors express their sincere thanks to the Head, Dept of Physics & Director of Govt Vidarbha Institute of Science and Humanities, Amravati for providing the necessary laboratory facilities during the progress of this work.

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Fig. 7. Variation of pre-exponential factor (-logσ0) versus Composition for the glass samples.

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CONCLUSION

The optical parameters such as absorption coefficient, optical dielectric constant, refractive index, optical energy gap, constant , measure of extent of band tailing, infinitely

88 W. J. Gawande, S. S. Yawale, and S. P. Yawale, ―Optical and electrical properties of CuO-MnO2-B2O3 glasses,‖ International Research Journal of Advanced Engineering and Science, Volume 2, Issue 3, pp. 85-88, 2017.